We have to consider one thing: we call PvE server an old server, but in fact, this is not at all. It's almost a new server considering the patchs timeline, i know plenty of ppl wants a pvp server, but for someone who wishes to go on a pve server, he's gonna play on a "fresh" server, almost everything is to discover, you just missed Dire Maul and Alterac release, that's all. When they announced the shutdown, PvE had 4/5 months. Think about it.
Edit: You missed Kazzak and Azuregos release too, but it doesn't mean that you won't be able to kill them at all, in Vanilla, whatever patch you are, all raids/dungeons are useful.